1. Field of the Invention
The present invention relates to a fixing device that is used in such image forming apparatus as copying machines, printers, facsimiles, etc. for fixing developer images that are formed on recording media.
2. Description of the Related Art
A conventional fixing device that is used in electro-photographic copying machines, printers, etc. has a separation member for separating sheet paper from a fixing roller after passing a fixing device. When this separation member is provided in contact with a fixing roller, streak traces and scratches rubbed by the separation member are produced on the surface of the fixing roller. These traces and scratches appeared on fixed images resulting in deterioration of image quality.
For example, in Japanese Patent Disclosure (Kokai) No. 7-181826, a device to separate a recording paper from a fixing roller by a non-contact separation guide using a curvature separation system is disclosed.
However, the above-mentioned non-contact separation guide may produce a separation error if a gap between it and a fixing roller is too large and to surely separate a recording paper, it is necessary to bring the separation guide to a fixing roller as close as possible. And to maintain a gap between the fixing roller and the separation guide that are closely mounted highly precise and to remove various factors affecting the gap, it is necessary to improve manufacturing and mounting accuracy of the fixing roller and to remove dimensional and mounting accuracy of the separation guide and furthermore, prevent oscillation of the fixing device when an image forming apparatus is driven so that a diameter of the fixing roller does not vary.
Accordingly, in a heating and pressure fixing device, a fixing device that is capable of surely separating sheet paper from a fixing roller, expanding a margin of manufacturing and mounting accuracy of a fixing roller and a non-contact separation member, suppressing increase in manufacturing cost and obtaining fixed images of high quality without causing trace of scratches of a fixing roller is desired.
An object of the present invention is to obtain a fixed image of high quality in a heating and pressing type fixing device by surely separating a sheet paper by a non-contact separating member without increasing a manufacturing cost.
According to an embodiment showing one example of the present invention, a fixing device comprises: a fixing member that is brought in contact with a developer image forming surface of a recording medium; a pressure member that press contacts the fixing member and conveys the recording medium by clamping it jointly with the fixing member; and a non-contact separating member that separates a recording medium after passing through a nip area formed between the fixing member and the pressing member, characterized in that r/Lxe2x89xa61 where r is a distance from an exit of the nip area to the separation edge of the separation member and L is the minimum value of the edge margin of a recording medium.